Dashpot



A. ROSCH DASHPOT May 27, 1941.

Filed June 26, 1940 Tsi. 3,

IhvecoT-, Arthur* Resch,

Patented May 27, 1941 Unis rar-.ss

DASHPOT Application .lune 26, 1940, Serial No. 342,595 In Germany July24, 1939 (Cl. 18S- 97) 2 Claims.

The present invention relates to dashpots comprising a cylinder with apiston movable therein and substantially filled with oil or like liquid.The upper and lower side of the piston communicate through a bypassusually including a valve. Such dashpots are used, for example, inisochronous governing mechanisms of the type disclosed in the Patent No.2,077,384 to Dettenborn, issued April 20, 1937, and assigned to the sameassignee as the present application. A dashpot broadly 'm suchmechanisms constitutes a link adjustable in its length and forming vpartof a restoring mechanism. In many instances it has been found that theperiod of time it takes for a certain amount of oil to be displacedthrough the by-pass connecting the lower and upper sides of the pistonis too long.

The object of my invention is to provide an improved construction andarrangement of dashpots whereby such period of time may be substantiallyreduced. This is accomplished in accordance with my invention by anarrangement which includes a by-pass offering a resistance to flow ofiluid therethrough which is automatically controlled in response tomovement of the dashpot piston.

For a better understanding of what I believe to be novel and myinvention, attention is directed to the following description and theclaims apf pended thereto in connection with the accompanying drawing.

In the drawing, Fig. 1 illustrates a dashpot embodying my invention;Fig. 2' is an enlarged detail View of a part of Fig. l; and Fig. 3 is anexplanatory View.

The arrangement comprises a cylinder II) with a lower end closed by acover II and held on a support I2. A piston I3 is movably disposedwithin the cylinder and has a lower end secured to a hollow stem I4. Thepiston in the present instance is in the form of a cylindrical elementwith a bottom portion integrally formed with the hollow stem IQ. Aspindle I5 has a portion slidably disposed within the hollow stem I4 andan upper portion secured to two sleeves I6 and Il, each having anannular iiange I8 and I9 respectively. A compression spring is disposedwithin the upper hollow portion of the piston and has lower and upperends engaging spring plates or washers 2l and 22 respectively. Thewasher 2l in the neutral position indicated engages a shoulder orannular projection 23 of the piston wall and also the flange I9. Theupper washer 22 engages a shoulder 24 on the piston and the annular angeI8. The shoulder 24 is formed by a flanged cup 25 threaded into theupper end of the piston wall. The cylinder Ill and the piston I3 dennetwo chambers, a chamber 26 below the bottom of the piston and a chamberl21 above the bottom of the piston and extending tothe upper ends of thespring. The two chambers communicate in known manner through a by-pass28 formed by bores in the side wall of the cylinder I. The lower end ofthe by-pass communicates with the chamber 26 through a groove 29 intheinner surface of the cylinder I0 and lwith the chamber 21 through a port30 formed in the piston side wall. The flow or displacement of fluidbetween the chambers 26 and 21 is adjustable by a needle valve 3i in theby-pass 28.

The operation of the dashpot described above is as follows: Suddendownward movement of the spindle I5 compresses the spring 2B, forcingthe upper washer 22 downward whereby the lower end of the spring and thewasher 2| cause gradual downward movement of the piston due to theengagement of the washer ZI with the shoulder 23, thereby displacing oilor other liquid contained in the lower chamber 2E through the bypass 28into the upper chamber 21 until the spindle and the piston have returnedto their original relative position in which the washers 2! and 22'engage the shoulders 23 and 24 respectively. The time delay betweenmovement of the spindle I5 and the follow-up action of the piston I3 isa function of the restriction to ow of liquid through the by-pass and isa fixed value for a given position of the needle valve 3l and a givenregulating action causing a certain impulse on the spindle. In manyinstances, as when such dashpots are used in connection with governingmechanisms controlling prime mover driven A. C, electric generators, itis important to reduce the delay of the dashpot action in order toreduce `frequency variations of the generator. As stated above, the timedelay of the dashpot is reduced in accordance with my invention by theprovision of a by-pass which is automatically controlled by movement ofthe dashpot piston, more speciiically by relative movement between thepiston and the spindle.

In the present instance the arrangement includes two pins 32 and 33.Each pin has a lower portion secured and sealed to the bottom of' thepiston and an intermediate portion slidably projecting through anopening 34 in the annular flange I9. Both pins act as guides for thespindle and the elements secured thereto, preventing rotary relativemovement between the spindle and the piston. The pin 33 in additiondefines a passage or auxiliary by-pass which in certain positionseffects direct communication between the chambers 26 and 21. Morespecically the pin 33 has a vertical bore 35 communicating at its lowerend with the chamber 26 and at its upper end through a cross bore 36with an annular recess or port 31 (Fig. 2) in the outer surface of thepin. This annular recess in normal position as indicated is completelyenclosed within the bore 34 of the ange I9. In fact the flange I9 in thepresent instance overlaps the recess 31 at both ends. y

For slight, relative movement between the piston and the spindle due toslight regulating impulses exerted on them the auxiliary by-pass 35, 36is ineffective. If the spindle I5 is moved relative to the piston asufhcient distance downward, the upper surface of the annular ange I9 ismoved below the upper end of the recess or port 34 and therebyestablishes direct connection between the chambers 26 and 21 through theauxiliary by-pass 35, 36, oil being permitted to flow from the chamber26 through the auxiliary by-pass 35, 3B directly into the upper chamber21; in addition, oil being by-passed in the usual manner from thechamber 26 through the main by-pass 28 into the upper chamber. 21.

Similarly, if the spindle I5 is moved upward relative to the piston asuflicient distance until the lower face of the annular flange I9uncovers the lower end of the recess 31, direct connection isestablished through the auxiliary by-pass and oil may flow from theupper chamber 21 through the bores 36, 35 into the lower chamber 26.With this arrangement the time delay during sudden considerable relativemovements of the spindle I5 is substantially reduced. This can best beseen from consideration of Fig. 3 in which the curve ABC illustrates themovement of the piston of a dashpot, as shown in Fig. 1, but without theauxiliary by-pass and curve ABD illustrates the movement of a similararrangement with an auxiliary by-pass as described above. The period oftime t1 in the latter instance is only about one-third of the period oftime t2 of the normal arrangement without the auxiliary by-pass.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. Dashpot arrangement comprising a cylinder, a piston movable in thecylinder and forming two chambers therewith, a spindle, means includinga spring connecting the spindle to the piston and normally maintaining axed relative position between them, and means including a pin secured tothe piston and a member secured to the spindle defining a by-pass havinga restriction to ow of fluid varying in response to relative movementbetween the piston and the spindle.

2. Dashpot arrangement comprising a cylinder, a piston movable in thecylinder and dening lower and upper chambers therewith, an adjustableby-pass connecting the chambers, a spindle projecting into the piston, aspring normally holding the spindle and the piston in xed relativeposition, a flange with a bore secured to the spindle, a pin secured tothe piston and having a central bore communicating with the lowerchamber, and a cross bore communicating with the central bore andnormally closed by the bore in the Iiange, said cross bore in a certainrelative position between the spindle and the piston establishing directcommunication between the lower and upper chanmbers.

ARTHUR BOSCH.

